It grows into a large shrub up to 12 feet tall, but with pruning in late winter it can be kept to as low as 4 feet. It is root-hardy in zone 6, so it grows and blooms well even there, and in colder zones it can be grown as a pot-plant and kept over winter in any cool, frost-proof place.

Lagerstroemia indica 'Black Diamond' Purely Purple
Black Diamond BL DMND